(a) Field of the Invention
This invention relates to retinal cameras and more particularly to an illuminating device for retinal cameras wherein the illuminating light amount to the retina is made controllable so as to be of a proper value.
(b) Description of the Prior Art
In a conventional retinal camera, in the case of strobo-photographing, as the object to be photographed is limited to a retinal part of an eye, the strobo-tube has been manually made to emit light while neglecting the difference in the reflection factor of the retinal part. However, in fact, the reflection factor is different depending on the eye to be inspected and, in the case of photographing the periphery of the retina, as the light bundle will be cut by the size of the pupil, the obtained photograph will not be always of a proper exposure. Even if the emitted light amount is corrected by assuming the cut of the light bundle, the operation will be difficult. Particularly, in a mass-diagnosis, the accuracy and operatability of the photographing are important. With a non-mydriasis retinal camera used recently in the mass-diagnosis, once the retina is photographed, the pupil will become so small that a time will be taken before it can be photographed again. Further, in the case of a natural mydriasis, the opening degree of the pupil will be so personally different that a cut will occur in some case and the exposure will be often wrong.
For the above reasons, it is generally desired to incorporate an autostrobo mechanism in a retinal camera. However, as the retina very low in the reflection factor is to be photographed, the exposure will be greatly influenced by the dispers and reflected lights within the eye, the light reflected on the cornea surface and the like. Such detrimental lights often appear from the periphery of the image plane. Particularly the dispersed and reflected lights at a wide angle are difficult to remove. Such detrimental lights are likely to enter the periphery of the image plane. Therefore, the light measuring range in the autostrobo-photographing had better be limited to be in the center part of the image plane. However, the reflection factor of the retina is not uniform. Particularly, the reflection factor of the nipple part is much higher than in any other part. Depending on the light measuring range, the exposure will be influenced by the variation of the nipple position with respect to the image plane.